\Header{length}{Length of a Vector or List}
\alias{length<\Rdash}{length}
\keyword{attribute}{length}
\begin{Description}\relax
Get or set the length of vectors (including lists).\end{Description}
\begin{Usage}
\begin{verbatim}
length(x)
length(x) <- value
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a vector or list.
\item[\code{value}] an integer.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
\code{length} is generic: you can write methods to handle of specific
classes of objects, see \link{InternalMethods}.

The replacement form can be used to reset the length of a vector.  If
a vector is shortened, extra values are discarded and when a vector is
lengthened, it is padded out to its new length with \code{\Link{NA}}s.\end{Details}
\begin{Value}
The length of \code{x} as an \code{\Link{integer}} of length 1,
if \code{x} is (or can be coerced to) a vector or list.  Otherwise,
\code{length} returns \code{NA}.\end{Value}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.\end{References}
\begin{SeeAlso}\relax
\code{nchar} for counting the number of characters in
character vectors.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
length(diag(4))# = 16 (4 x 4)
length(options())# 12 or more
length(y ~ x1 + x2 + x3)# 3
length(expression(x, {y <- x^2; y+2}, x^y)) # 3
\end{ExampleCode}
\end{Examples}

